Performance Based Navigation (PBN) – Why the “N” Should Be an “O”

The abbreviations game

In aviation we seem to be creating abbreviations at a rate that raises the specter of our grandchildren not having any usable combinations left any more. This remark from a well respected colleague of mine who used to work for UPS airlines does in fact indicate a few problems that go beyond the scarcity of available unique letter combinations and which, PBN backlinks as we will see, affect our daily work in all kinds of unexpected ways.

Consider the well known CNS formation which, we all know, stands for Communications, Navigation and Surveillance. Whoever came up with the abbreviation CNS probably had no idea how much damage their invention would cause in air traffic management by perpetuating the kind of silo mentality that keeps many organizations hopelessly divided and some experts retreating into their respective ivory towers.

If at least the inventors had the good sense of putting those letters into some kind of logical order, like history, which would have given us NCS… We did navigate first (as in trying to find our way by reading the names of train stations and flying along highways), then communicated, initially with lights and hand signals and later via radio and most recently we do surveillance also. Not that NCS would have been any better at driving the silo mentality from the face of the earth.

Of course in the old days there was some logic in looking at navigating and communicating as something totally different from each other. You trained for one or the other, aircraft carried separate navigators and radio operators and when radar came along, the wizards of that kit were a completely new breed yet again. It was only logical also that separate fiefdoms should grow up along the letters NCS with hardly any horizontal contact between them. That they should fiercely protect their respective domains was perfectly natural…

Let’s now jump forward a few decades to arrive in our own brave times where CNS still rules, the fiefdoms are mostly there still… OK, so where is the problem? The problem is, while the CNS organization stayed mostly the same, the world around it has completely changed. Looking at air traffic management along a CNS organization is like hanging the TGV (High Speed Train) behind a steam locomotive and wondering why there is so much smoke with the train only crawling along.

Look at GPS. This clever system does only two things: it gives you precise time and signals from which you can calculate a position fix. What letter of the magic trio would you allocate to that? We broadcast augmentation signals to the aircraft to make the GPS position fix even more accurate, using a VHF digital link… Is that C or N or S??? Finally, the aircraft will broadcast its GPS derived position for other aircraft and the ground to use in a number of ways. Well, at least that is clear, we are talking about S for surveillance, right? Partly yes but a position can be, and is being, used for many other purposes that fall way outside the traditional definition of surveillance.

Our world has evolved into a data based enterprise and air traffic management is no exception. In the GPS example, basically the same data is being used and re-used and it is the end-user applications that determine whether it ends up being part of navigation or surveillance… or communications for that matter. The air traffic management world is not about communications, navigation and surveillance. It is about data that can be any of the famous C or N or S without the need, or indeed the possibility, to erect silos around it.

What is wrong with PBN?

Recently we had a very successful workshop on PBN and the agenda included a presentation on modern surveillance techniques and another on cost-benefit analyses tailored to performance based systems. It was soon clear that several experts thought that the surveillance presentation was out of place in a meeting on Performance Based Navigation. After all, PBN is dealing with navigation and not surveillance, they said.

There you go, the good old silo mentality again! Thou shall not mix things from different silos!

Do a local reality check. How is your organization set up? Do you have separate departments for navigation, surveillance and communications? Ask someone from surveillance or communications what PBN stands for… Chances are they will not know or if they do, they will consider it the business of someone else.

PBN traces its ancestry to RNP which was/is of course Required Navigation Performance. There the N did make sense as RNP was indeed about navigation performance and not more. But when the idea was expanded and applied to performance based systems generally, the N became a limitation, an excuse for many to think they were not concerned with it.

The inventors of the term PBN meant well, no doubt about that. But by not thinking through how much wider than just navigation the concept they were introducing really was, they laid the foundation of the exact silo approach we are all working so hard to break down. The result? People on the surveillance or communications side of the business tend to ignore PBN, thinking it is creating requirements only for navigation and that is not their desk. Even worse, some experts in air traffic management operational concept work also tend to ignore PBN, convinced that they will get the requirements from the navigation experts… and so on. Silos once built are notoriously difficult to break down and environments sprouting from silos are notoriously poor at fulfilling their tasks.

The pretty wide-spread uncertainty about what PBN really means and to whom and why, is a good indicator of the height to which the silos have already been erected. And all this because of the N in PBN. One third of the abbreviation is wrong.

Now what about changing the N to an O and calling the new concept Performance Based Operations? Instead of focusing on just navigation, PBO could be the frame stretching horizontally and unifying the requirements set against communications, navigation and surveillance plus all the other things that need to be considered for a good performance based system.

Most of the current PBN documentation could survive with only minor changes, so no problem there. A lot of new material would need to be written of course and that might be a problem… But again it might not. After all, PBO would not be seen as concerning the other guy only and who would want to be left out of this brave new world?

The magic of PBO

Now imagine a world where Performance Based Operations are central to air traffic management and all the requirements for data of all kinds are derived from PBO. In this vision, there are no silos any more. PBO unifies all the disciplines in a performance based framework.

What are the elements of PBO?

Trajectory based operations (TBO) is perhaps the best example of this unified framework paradigm. TBO involves very accurate navigation performed by the aircraft, accurate surveillance on the ground and eventually in the air, and a net-centric environment which ensures that all data relevant to TBO is safely shared and accessible to those concerned at all times.

Even if we have not yet been successful in getting rid of the CNS silos, it is clear that PBO requires a bit of all of the well known disciplines if we are to move forward. Navigation on its own cannot save the day, no matter how powerful PBN may otherwise be. But neither can surveillance or communications on their own as such.

Together, united by the data based paradigm and integrated under the PBO framework they can and will support all the requirements posed by air traffic management.